The electrocardiogram (ECG) is a representation of electrical activity of the heart. An ECG signal may be represented by multiple key points of clinical relevance such as QRS, P wave and T wave. The QRS-complex is considered to be the most important waveform in an ECG signal. The QRS-complex includes three characteristic points within one cardiac cycle denoted as Q, R and S. R-peak in such QRS complex is one of the most pivotal points to analyze an ECG signal. Therefore, detection of the QRS-complex is fundamental to the analysis of an ECG signal. Although detection of the QRS-complex is not a problem, noise, pathological signals and variations in amplitudes may result in significantly reduced accuracy and faulty detection of the QRS-complex.
Currently, R-peak in an ECG signal may be detected by several methods. These methods make use of derivative feature responses. Such derivative features are computed and compared against the pre-defined threshold after non-linear filtering to accomplish R-peak detection. For example, in one of the methods for detection of the QRS-complex, the Teager Energy Operator (TEO) is employed to detect characteristic points of the ECG signal. TEO reflects the instantaneous frequency and instantaneous amplitude changes in the signal. The TEO is employed to restrain the P wave, the T-wave, the powerline interference and the baseline wander in an ECG signal. The energy operator uses data obtained from three adjacent sample points. The output of the TEO is proportional to the product of the amplitude and the frequency of the input signal.
However, the method of detection of R-peak point using the TEO has several disadvantages. The method obtains close to 99% QRS complex detection rate on MIT/BIH arrhythmia database. Contrarily, this method fails to provide accurate results where variations in the ECG signal are more than MIT/BIH dataset. Several detections of R-peak points have been faulty, and many R-peak points have been missed. The TEO response in such cases is not very distinctive for T-peak and R-peak. Setting a single threshold for the computed responses is difficult due to the instability.